Help! Oil pressure dropping under acceleration

[Jim Yergin]

According to the master parts book on Chet's site, Joe is correct. Green is heavy duty, red is light duty and plain is standard duty.

The same parts are listed for all years 1936-1948.

Jim Yergin

[chipdeson]

I just recently experienced the exact same thing. Oil pressure would decline significantly as rpm went up under acceleration. The oil pressure caught up pretty quickly, but it was starting to worry me. I don't drive the car a lot of miles, so it had been way too long since an oil change. I was running 30W before, but changed it to 20/50 with a new filter. The problem was completely gone. Running oil pressure is slightly higher than with the old 30W (higher than 40 lbs.) and idling oil pressure only dropped slightly (a little under 40), and the oil pressure immediately increases with RPM. Can't explain it, and these other guys know a lot more than me, but in my case it worked with no other changes. Good luck.

[Don Coatney]

Pictured is the replacement spring I installed in my Desoto engine after the original spring broke. New spring is unpainted and two inches long.

[rustyzman]

A loss of oil pressure under high rpm that comes back at idle sounds like oil starvation at the pump. Pickup screen could be sludged over allowing little oil in when demand is low and not enough oil in when demand is high. An air leak in the pickup tube is also possible. If you have an inch of sludge in the bottom of the pan, your capacity could be low enough to uncover the pickup pivot and suck air.

Low oil pressure can come from several sources. Bearing clearances are critical to maintaining oil pressure. Even your idle pressure seems very low at 5-10lbs. If this is a hot only problem, and oil pressure is good at cold and warmup, I would start with the relief valve. If it looks worn or the spring is bent/weak/broken, replace them and see where you stand.

If it is low all the time, suspect worn pump or worn bearings. Heavier oil may improve this a little, but it will simply cure the symptom, not the problem.

If the engine has not been apart or rebuilt in recent times removing the oil pan and cleaning the sludge from the bottom and the pickup screen would be very important.

If you have no knocking, rod bearings are likely not completely shot, though they could be worn. Main bearings could be worn and have excess clearance where you may not even hear it. That would definately create a low oil pressure condition.

Don't forget the possibility that your gauge is faulty. If the engine gets noisy when it occurs, it is probably legit, but checking with an oil pressure test gauge may not be a bad idea.

The oil pump itself could also need a rebuild/replacement.

Sorry for so many possibilities, but without disassembly and inspection it is almost impossible to say for sure what is wrong.

Hope it helps.

[Young Ed]

I've always heard these engines loose oil pressure at the cam bearings first and then the others follow. Be aware of that if you decide to tear into it for bearings.

[rustyzman]

Good point Ed. If you are in the engine and determine the need for any bearings, a rebuild or at least replacement of all bearings would be wise. Chances are if one area is worn, the rest are too.

[aero3113]

Hey guys, Joe was not able to find his plunger for me. Anyone have one they would like to get rid of with a spring?

[jd52cranbrook]

Shel Bizzy, I read that post, but that really seems to be the opposite issue, stepping on the gas makes my problem get worse, and the engine will start to make some... distressing noises, as if it were running without oil. As soon as I let off the gas and let it coast it will go back up to around 5 or 10 PSI and not sound so rough. I did check my oil level and it was alright.

How do I get at the screen on the oil pick up assembly? Do I have to drop the whole pan or is there a way for me to get at it from the outside?

Just wondered if you have found a solution as yet?

[aero3113]

The plunger is what I think the problem is. This week I will make some calls and see if anyone carries them.

[jd52cranbrook]

How bout you ActionGrant? Any news on the low oil pressure?

[aero3113]

Just called Vintage Power Wagons, they are sending me a used plunger and spring (good condition) for $15. Will let you guys know how it works out when I get it installed.

[jd52cranbrook]

Good to hear areo

Did I miss something, was the original author's problem fixed? I'd like to know what caused it.

[aero3113]

Not sure,I kinda hijacked the thread. Sorry ActionGrant

[Joe Flanagan]

Well, aero, if you ever want to try out a heavy duty spring, I have an extra. Still don't know what I did with that doggone plunger, though. It'll probably turn up right around the time yours arrives in the mail.

[Cpt.Fred]

once again a very interesting thread, thanks to all people involved!

i know a certain person that will adjust valves tonight,

and i have a feeling this person will take the relieve valve out for a little checking and cleaning

to see if the oil pressure rises afterwards as long a sthe hands are dirty anyway...

[Joe Flanagan]

Good idea, Fred. As you may recall, my valve was stuck in its bore after sitting for seven years after a rebuild. Ten pounds of oil pressure was all I could get no matter what I did. After a quick cleanup all was well.

Report back on how the valve adjustment goes.

[Cpt.Fred]

alright, bull's eye. i opened the release valve plug and the spring slid out in 4

(in words: FOUR) pieces.

i'm beginning to think bad thoughts about this engine...

i didn't get the plunger out, but i could feel it moving, so it's not stuck completely.

how did you get yours out???

i took the largest piece of the spring and put a small screw with the head down into the plug.

oil pressure shoots right up to 40 at idle, climbing even more when i rev it, 60-65.

engine wasn't hot, though, but this looks a lot better now.

how much is too much?

joe, i use your valve thread for my valve story, if that's ok with you...

[Joe Flanagan]

In past threads, it's been recommended to drive a self-tapping screw into the plunger and pull it out. Apparently this does no harm to the plunger itself. I tried that and had no success. I couldn't get the screw to penetrate the plunger. I was probably not using the right type of screw, though. In the end, it loosened up enough for me to pull it out with my fingers. I've also read that you can crank the engine and the oil pressure will force it out. I had no luck with that either, though.

[Cpt.Fred]

me neither, cranking and even starting didn't force it out.

well, it's moving and i have more pressure now,

so maybe i just leave it there for now.

[Joe Flanagan]

But you still need a spring, correct?

It's amazing. I had the same thing happen to me. The spring was intact but the valve wouldn't move.

[Merle Coggins]

Could there be a small piece of your broken spring laying in there and keeping the plunger from coming out? Can you fish a small magnet around in there to see if any more bits come out?

I've also had good luck on other valves, when I need to pull a plunger out, by using a snap ring pliers with a long nose. I have a pair for transmission lock rings that have wider jaws and work well. Put the working end of the pliers into the plunger and squeeze the handles. This spreads the jaws against the inside of the plunger and grips it. Now pull it out.

Merle

[Joe Flanagan]

Yeah, I was thinking of something similar. Snap ring pliers should do the trick.

[Cpt.Fred]

a friend of mine will bring me one this evening (hopefully, so i can do a little more fishing. good idea!

i took a small mirror and a flashlight to look inside the plunger's hideout.

i couldn't see or feel any more pieces of the spring.

when i put the pieces next to each other, they add up to approximately 2",

which should be the right size if i recall that correctly.

the screw i used lays its head snugly inside the plug and is about 1" long,

the biggest piece of spring is fitting around the threads and now has enough

pressure to hold the plunger down with more force than before.

i'll try get a new spring somewhere, maybe stovebolt or even ford V8 parts will fit, who knows?

gotta make some calls...

anyway, i'm happy to know now. once again, thanks everyone!

[insaneradio]

oil pressure shoots right up to 40 at idle, climbing even more when i rev it, 60-65.

engine wasn't hot, though, but this looks a lot better now.

how much is too much?

QUOTE]

That is where mine has ran for as long as I have owned my car. I too have always wondered if this was too much. I hope someone chimes in!

Dave

[james curl]

I pulled a stuck plunger by forcing a piece of dowel rod into it and rotating the dowel rod and freeing the plunger. When I rebuilt my engine before having it hot tanked I lapped the plunger into the seat with valve grinding compound, then washed it out with paint thinner before it was hot tanked. I too broke a spring after the engine was rebuilt, the oil pressure kept going lower until I pulled the cover off of the by pass valve and found the spring in three pieces.